diff --git a/components/net/image_cache.rs b/components/net/image_cache.rs
index 2f0968f3aa4..d7dc1e171d6 100644
--- a/components/net/image_cache.rs
+++ b/components/net/image_cache.rs
@@ -41,6 +41,7 @@ use crate::resource_thread::CoreResourceThreadPool;
 // ======================================================================
 
 fn decode_bytes_sync(key: LoadKey, bytes: &[u8], cors: CorsStatus) -> DecoderMsg {
+    // decode
     let image = load_from_memory(bytes, cors);
     DecoderMsg { key, image }
 }
diff --git a/components/script/dom/domexception.rs b/components/script/dom/domexception.rs
index c058136a8b5..2267148626f 100644
--- a/components/script/dom/domexception.rs
+++ b/components/script/dom/domexception.rs
@@ -41,6 +41,7 @@ pub enum DOMErrorName {
     TimeoutError = DOMExceptionConstants::TIMEOUT_ERR,
     InvalidNodeTypeError = DOMExceptionConstants::INVALID_NODE_TYPE_ERR,
     DataCloneError = DOMExceptionConstants::DATA_CLONE_ERR,
+    EncodingError,
     NotReadableError,
     OperationError,
 }
@@ -70,6 +71,7 @@ impl DOMErrorName {
             "TimeoutError" => Some(DOMErrorName::TimeoutError),
             "InvalidNodeTypeError" => Some(DOMErrorName::InvalidNodeTypeError),
             "DataCloneError" => Some(DOMErrorName::DataCloneError),
+            "EncodingError" => Some(DOMErrorName::EncodingError),
             "NotReadableError" => Some(DOMErrorName::NotReadableError),
             "OperationError" => Some(DOMErrorName::OperationError),
             _ => None,
@@ -115,6 +117,9 @@ impl DOMException {
                 "The supplied node is incorrect or has an incorrect ancestor for this operation."
             },
             DOMErrorName::DataCloneError => "The object can not be cloned.",
+            DOMErrorName::EncodingError => {
+                "The encoding operation (either encoded or decoding) failed."
+            },
             DOMErrorName::NotReadableError => "The I/O read operation failed.",
             DOMErrorName::OperationError => {
                 "The operation failed for an operation-specific reason."
diff --git a/components/script/dom/htmlimageelement.rs b/components/script/dom/htmlimageelement.rs
index 80c016b6b9d..2b60b93203a 100644
--- a/components/script/dom/htmlimageelement.rs
+++ b/components/script/dom/htmlimageelement.rs
@@ -5,6 +5,7 @@
 use std::cell::Cell;
 use std::collections::HashSet;
 use std::default::Default;
+use std::rc::Rc;
 use std::sync::{Arc, Mutex};
 use std::{char, i32, mem};
 
@@ -47,6 +48,8 @@ use style::values::specified::AbsoluteLength;
 use style_traits::ParsingMode;
 use url::Url;
 
+use super::domexception::DOMErrorName;
+use super::types::DOMException;
 use crate::document_loader::{LoadBlocker, LoadType};
 use crate::dom::activation::Activatable;
 use crate::dom::attr::Attr;
@@ -84,6 +87,7 @@ use crate::dom::node::{
     UnbindContext,
 };
 use crate::dom::performanceresourcetiming::InitiatorType;
+use crate::dom::promise::Promise;
 use crate::dom::values::UNSIGNED_LONG_MAX;
 use crate::dom::virtualmethods::VirtualMethods;
 use crate::dom::window::Window;
@@ -1605,6 +1609,26 @@ impl HTMLImageElementMethods for HTMLImageElement {
         }
     }
 
+    /// <https://html.spec.whatwg.org/multipage/embedded-content.html#dom-img-decode>
+    fn Decode(&self) -> Rc<Promise> {
+        // Step 1
+        let promise = Promise::new(&self.global());
+
+        // Step 2
+        let document = document_from_node(self);
+        if !document.is_fully_active() {
+            promise.reject_native(&DOMException::new(
+                &self.global(),
+                DOMErrorName::EncodingError,
+            ));
+        } else if self.current_request.borrow().image.is_some() {
+            promise.resolve_native(&());
+        }
+
+        // Step 3
+        promise
+    }
+
     // https://html.spec.whatwg.org/multipage/#dom-img-name
     make_getter!(Name, "name");
 
diff --git a/components/script/dom/webidls/HTMLImageElement.webidl b/components/script/dom/webidls/HTMLImageElement.webidl
index 0d242fefb26..faae1c8992b 100644
--- a/components/script/dom/webidls/HTMLImageElement.webidl
+++ b/components/script/dom/webidls/HTMLImageElement.webidl
@@ -29,6 +29,9 @@ interface HTMLImageElement : HTMLElement {
   readonly attribute USVString currentSrc;
   [CEReactions]
            attribute DOMString referrerPolicy;
+
+  Promise<undefined> decode();
+
   // also has obsolete members
 };